This invention relates to solar collectors and more particularly to a low cost solar air heater employing jet impingement concepts for high collection efficiency.
Solar air heaters offer the potential of significant energy savings in application where process hot air is required such as the drying of lumber, paper, and food (raisins, prunes, grain) and for winter air heating in areas such as the southwestern region of the United States Unfortunately, present-day solar air heaters or solar collectors exhibit relatively low collection efficiencies, are relatively heavy, and are expensive to construct and install, thus leading to rather high cost of collected solar energy.
In one typical prior art solar air heater, air is heated by causing it to flow in a serpentine path past a flat absorber plate which is mounted beneath one or more glass panes and absorbs solar radiation. The heat transfer coefficient for exchange of heat between absorber plate and air for this configuration is rather low, resulting in less heating of the air than desired and also in a high absorber plate temperature and hence high radiative and convective losses. Use of multiple panes of glass can reduce these losses but lowers transmission of incident radiation and adds to cost. Attachment of fin structures to the absorber plate increases heat transfer to the air but also increases design complexity and cost.
Another source of inefficiency in the conventional design described above is the large total pressure drop resulting from the many bends the air stream must make in passing through the collector, which leads to high costs of the blower/motor used to circulate the air through the collector. Still another drawback is the need for substantial amounts of insulation in the base of the collector to avoid large thermal losses since in the conventional solar air collector the base remains in direct contact with the air as it is progressively heated.
Accordingly, it is an object of the invention to provide a low-cost, efficient solar collector for heating air.
It is another object of the invention to provide a solar collector wherein impingement of air jets on an absorber plate of the collector results in efficient transfer of heat between air and the absorber plate.
It is a further object of the invention to provide a solar collector with jet impingement wherein after impingement the spent jets are discharged from the collector with minimum interference with downstream impinging jets.